We present a three-dimensional S-velocity model for the upper mantle beneath the Philippine Sea region. It was derived from inversions of 281 broad band vertical-component seismograms recorded in the area at the Global Seismological Network (GSN) and SKIPPY portable array stations. We have been able to obtain high-resolution tomographic images spanning the depths down to 200--300 km and locally down to the upper transition zone. High-velocity subducting slabs and low-velocity volcanic arc regions are the dominant features of the model. Fast, thin lithosphere of back-arc basins is underlain by a prominent low-velocity zone. Low velocities at lithospheric depths are observed beneath the extinct Central Basin Ridge in the West Philippine Basin and close to the Eauripik Ridge that separates the East and West Caroline basins. High upper-mantle heterogeneity and resulting scattering presents a difficulty and limits the resolution, especially below 200--300 km. Explicit modeling of seismic wave diffraction may be necessary for a significant improvement in resolution.¿ 1997 American Geophysical Union